Gas

In physics, a gas is a state of matter, consisting of a collection of particles (molecules, atoms, ions, electrons, etc.) without a definite shape or volume that are in more or less random motion. Gasses are generally modeled by the ideal gas law where the total volume of the gas increases proportionally to absolute temperature and decreases inversely proportionally to pressure.

For more, visit the Wikipedia entry for gas, URL: http://en.wikipedia.org/wiki/Gas